Abstract
The tensile deformation behaviour of high-purity niobium single crystals has been evaluated at temperatures between 4·2 and 77 K. An athermal plateau in the yield and thermal stresses between 40 and 77 K has been demonstrated. Anomalies were observed in the strain-rate sensitivity at all temperatures within this plateau region. Alloying with 1 at.% Mo or 10 at.% Ta eliminates the plateau, although anomalous slip remained the dominant mode of deformation. The significance of these observations is discussed in the light of an interpretation of the mechanisms of anomalous slip, involving a transition from athermal to thermally activated control of plastic flow.